Distance increasing with temperature!

[discspeed]

Today it go into the 80s for the first time of the year. It was also as humid as its been this year. Its barely been in the 70s and very dry, and I was noticing a significant distance increase in my throws. It was most noticeable with my mids and putters, but I was throwing around 30' farther than I was getting when it was in the 50s. It was fun as hell to just watch my shots hang in the air. Its incredible how much air temperature, humidity, and air pressure have on disc flight.

 

[Roy]

I hear you bro. For me up in Wisconsin, it's really great to throw without boots and bulky clothing. I forgot what it's like to throw in a teeshirt and regular shoes. Let alone snow and ice.

80's is a bit warm for me. I wouldnt complain though :lol:

 

[Parks]

Its not just the clothes, its the air composition itself.

That being said, a lot of my longest throws are at an astroturf football field that is lit up at night.

I think a lot of that has to do with footing and the relaxed atmosphere, even if it is colder at night.

 

[Mad Scientist]

80's, huh? Must be nice. It's still lingering in the high 40's, low 50's here

 

[JHern]

Humidity is way way way more important than temperature. When its humid, you have more light weight H2O molecules occupying the same volume relative to N2 molecules. The weight difference is extreme, and brings the air density down quite a lot. And air density is the most relevant factor about the air for governing disc dynamics.

Lower weight molecules=lower density=lower air resistance. All discs will fly like faster versions of themselves.

 

[mafa]

Humidity is way way way more important than temperature

I don't think this is correct. For air density, temperature and air pressure are significantly more important than humidity. Sure humidity has a non-negligible effect but it's small. If you look at the varying conditions people disc golf (-20 F to 120F) and 0 ft to 6000+ ft elevations, the first two factors dominate with respect to air density and subsequent aerodynamic behavior of discs.

Matti

 

[JHern]

Humidity is way way way more important than temperature

I don't think this is correct. For air density, temperature and air pressure are significantly more important than humidity. Sure humidity has a non-negligible effect but it's small. If you look at the varying conditions people disc golf (-20 F to 120F) and 0 ft to 6000+ ft elevations, the first two factors dominate with respect to air density and subsequent aerodynamic behavior of discs.

Matti

Have you ever been to Florida? Altitude variation=0-10m (no change in air density). Typical temperature varies from 15-30C (change in air density is ~2%). Humidity varies (from dry to wet season) from as low as 10% to 100% relative humidity (change in density of up to 10%).

 

[Frank Delicious]

JHern really knows his stuff, just putting that out there.

 

[jubuttib]

Typical temperature varies from 15-30C (change in air density is ~2%).

How much is the change if temperature varies from -25C to +25C? Is it linear or exponential?

 

[tigel]

80's, huh? Must be nice. It's still lingering in the high 40's, low 50's here

story of my fucking life.

 

[rusch_bag]

80's, huh? Must be nice. It's still lingering in the high 40's, low 50's here

story of my fucking life.

Word.

 

[riverboy1]

It has been 40s here and I love it. Then again, I am kind of a freak when it comes to temperature preferences.

 

[Monocacy]

Typical temperature varies from 15-30C (change in air density is ~2%).

How much is the change if temperature varies from -25C to +25C? Is it linear or exponential?

Linear relative to absolute temperature in degrees Kelvin. To convert from degrees Celsius to degrees Kelvin, add 273.15.

In your example, a temperature change from -25C to +25C is equivalent to a change from 248.15K to 298.15K. Percentage-wise, this is roughly a 20% change in temperature. All else equal, air density would also change by approximately 20% (colder air being more dense).

All else is not equal, of course. Evaporation increases at higher temperatures, so warmer air typically holds a higher percentage of water vapor. As JHern pointed out, higher moisture content reduces air density.

 

[jubuttib]

Typical temperature varies from 15-30C (change in air density is ~2%).

How much is the change if temperature varies from -25C to +25C? Is it linear or exponential?

Linear relative to absolute temperature in degrees Kelvin. To convert from degrees Celsius to degrees Kelvin, add 273.15.

In your example, a temperature change from -25C to +25C is equivalent to a change from 248.15K to 298.15K. Percentage-wise, this is roughly a 20% change in temperature. All else equal, air density would also change by approximately 20% (colder air being more dense).

All else is not equal, of course. Evaporation increases at higher temperatures, so warmer air typically holds a higher percentage of water vapor. As JHern pointed out, higher moisture content reduces air density.

Thanks. Evaporation does increase when it's warmer and also warm air can contain more water than cold air, for example here in Finland the relative humidity is around 65% most of the summer and around 90% most of the winter (5 year averages. Okay, I took the figures for my city, geographical conditions will affect that, we're far inland). Regarding the amount of water molecules in air and how it affects density, is the absolute amount (higher in the summer due to more evaporation) or the relative humidity (higher in the winter because cold air can't contain as much water wapor) more important?

So in summary, the air is at its least dense on a hot (hot air being less dense and being able to contain more water, more water meaning less density) and misty (humidity ~100%, mist forms when there are suitable condensation centers in the air and when the air has more water than it can contain, often due to a drop in temperature) day. In these conditions everything flies like a faster version of itself, usually meaning more to the overstable side and effectively simulating a higher altitude. Did I get that right or did I miss something? It's 5:00AM so my brain might be a bit muggy.

 

[Monocacy]

Regarding the amount of water molecules in air and how it affects density, is the absolute amount (higher in the summer due to more evaporation) or the relative humidity (higher in the winter because cold air can't contain as much water wapor) more important?

Absolute amount. Relative humidity is a ratio: (partial pressure of water vapor) / (saturated vapor pressure of water at a particular temperature). In other words, cold air may have low moisture content but high relative humidity; hot air can have high moisture content with low(ish) relative humidity. Per Wikipedia, air can hold up to 3% water by mass at 30 C, but only 0.5% by mass at 0 C.

So in summary, the air is at its least dense on a hot (hot air being less dense and being able to contain more water, more water meaning less density) and misty (humidity ~100%, mist forms when there are suitable condensation centers in the air and when the air has more water than it can contain, often due to a drop in temperature) day. In these conditions everything flies like a faster version of itself, usually meaning more to the overstable side and effectively simulating a higher altitude. Did I get that right or did I miss something? It's 5:00AM so my brain might be a bit muggy.

Sounds right to me, except condensation on your disc might affect flight (and grip, of course). :wink:

 

[JHern]

So in summary, the air is at its least dense on a hot (hot air being less dense and being able to contain more water, more water meaning less density) and misty (humidity ~100%, mist forms when there are suitable condensation centers in the air and when the air has more water than it can contain, often due to a drop in temperature) day. In these conditions everything flies like a faster version of itself, usually meaning more to the overstable side and effectively simulating a higher altitude. Did I get that right or did I miss something? It's 5:00AM so my brain might be a bit muggy.

Sounds right to me, except condensation on your disc might affect flight (and grip, of course). :wink:

Right, temperature and humidity are coupled,, in that rising temperature allows more water vapor to be dissolved in the air. So the two effects relevant to Florida (temperature and vapor content) aren't independent from one another.

Mist or fog might not be a good thing, though, since it implies the existence of tiny drops of water, which have a much larger density than air, and which are in suspension in the air. You want 99.99999999...% relative humidity, with no fog or mist yet formed. That'll give you the lowest density at any temperature.

Note that the laminar viscosity of air can also decrease with increasing humidity (at constant temperature). This is explained by the classical theory of air viscosity, which involves transfer of momentum between particles in adjacent layers moving at different velocity. If the molecular mass is smaller, then the momentum transfer between the two layers is smaller for each particle that moves between the two layers (under random Brownian motion) than in the case of a nitrogen atmosphere (most of air on Earth is nitrogen). However, the laminar viscosity of air is less relevant for flow in the turbulent regime, where the Reynolds stress (density times dyad product of velocity fluctuations) dominates. So long as the disc is in the turbulent regime, density is the most important parameter of the air.

 

[mafa]

Humidity varies (from dry to wet season) from as low as 10% to 100% relative humidity (change in density of up to 10%)

Please do not confuse absolute and relative humidities. As Monocacy said, at 30C air can only hold 3% per weight water. Calculated examples at 1000 mbar actual air pressure:

Air densities at 30C with 10% and 100% RH are 1.15 and 1.13 g/l respectively
Air densities at 15C with 10% and 100% RH are 1.21 and 1.20 g/l respectively
Air densities at 0C with 10% and 100% RH are 1.28 and 1.27 g/l respectively
Air densities at -15C with 10% and 100% RH are 1.35 and 1.35 g/l respectively

It is clear that that temperature dominates and humidity has smallish effect. For example in jubuttib's climate conditions there's max 20% change in air density throughout the year due to the temperature variation.

Matti

 

[jubuttib]

Absolute amount. Relative humidity is a ratio: (partial pressure of water vapor) / (saturated vapor pressure of water at a particular temperature). In other words, cold air may have low moisture content but high relative humidity; hot air can have high moisture content with low(ish) relative humidity. Per Wikipedia, air can hold up to 3% water by mass at 30 C, but only 0.5% by mass at 0 C.

Yeah, I know, I worked as a flight weather observer for around 7 months. I thought it was the absolute amount but just wanted confirmation, so thanks.

Sounds right to me, except condensation on your disc might affect flight (and grip, of course).

Right, temperature and humidity are coupled, in that rising temperature allows more water vapor to be dissolved in the air. So the two effects relevant to Florida (temperature and vapor content) aren't independent from one another.Mist or fog might not be a good thing, though, since it implies the existence of tiny drops of water, which have a much larger density than air, and which are in suspension in the air. You want 99.99999999...% relative humidity, with no fog or mist yet formed. That'll give you the lowest density at any temperature.

Now that I'm sort of awake I see I meant to write "almost misty". The reason I mentioned condensation centers was to make the point that it's theoretically possible to have 100% relative humidity without any mist, takes ideal conditions but it's possible (and I was by hypothetical anyway ). In reality it's of course best to stay under 100%. Also water doesn't truly dissolve into the air, but does mix with it.

And mafa, am I just thrown off by your name or are my conditions in fact pretty much the same as yours?

 

[mafa]

And mafa, am I just thrown off by your name or are my conditions in fact pretty much the same as yours?

8000 km NE from Florida, temperature 2 C and relative humidity 100%?

Matti

 

[JHern]

Also water doesn't truly dissolve into the air, but does mix with it.

Dissolution=complete mixing down to the molecular scale. Yes, water does dissolve into air.